Traumatic brain injury can have severe deleterious consequences that may persist for decades following the initial injury. Whilst changes to individuals’ physical abilities may be most readily observed, cognitive difficulties are some of the most prominent impairments following TBI. They have been shown to lead to difficulties reintegrating into the community—including returning to competitive employment, study, and social functioning. Nevertheless, relatively little is known regarding the extent to which concurrent cognitive abilities influence the magnitude or rate of functional recovery. In turn, there is still limited understanding of the factors that underpin and maintain cognitive impairment following TBI. As such, this dissertation aimed to examine the following: 1) The progression of functional outcome over the first year following TBI, and its relationship with personal characteristics and cognitive performance, and 2) To examine the utility of several new magnetic resonance imaging techniques in identifying injury-related brain changes, and their relationship with severity of injury and cognitive performance. The present dissertation demonstrated that in a sample of individuals with mild-to-severe TBI, older age, lower education, and longer post-traumatic amnesia were associated with poorer functional outcome over the first year following injury. Cognitive performance contributed uniquely to functional outcome over the first year over and above these other factors, with performance in the executive function domain most strongly associated with the progression of functional outcomes. In demonstrating that cognitive deficits were significantly related to outcomes over the first year following TBI, this dissertation examined the brain changes underpinning these impairments. Using a semi-automated image analysis method, widespread reduction in regional grey matter volume was found following TBI, a trend that increased with more severe TBI. Poorer retention of newly learned material, working memory, and executive functions were associated with reduced cortical volume in frontal, parietal, and occipital brain regions. Using diffusion tensor imaging, it was also apparent that individuals with moderate or severe TBI displayed significantly poorer white matter integrity compared to healthy controls. Information processing speed and executive abilities were related to the integrity of several white matter tracts, including the superior and inferior longitudinal fasciculi, the internal capsule, and the corpus callosum. Lastly, the findings of this dissertation showed that susceptibility weighted imaging was superior to fluid attenuated inversion recovery in detecting the presence of lesions following mild-to-severe TBI. Susceptibility-weighted imaging quantified greater lesion volumes in both cortical and subcortical regions, and these were more strongly related to severity of injury. Nevertheless, both susceptibility-weighted imaging and fluid attenuated inversion recovery sequences showed that higher lesion volume was related to poorer memory and information processing speed. The findings of this dissertation are important, firstly in their demonstration that cognitive functioning significantly influences functional outcome following TBI. Subsequently, this dissertation highlights that several modern MRI techniques can be used to characterise the underlying pathology following TBI that is responsible for the production and maintenance of cognitive deficits.